This invention relates to extractors useful for liquid extraction processes. In particular, the present invention relates to the combination of features for improving the capacity and/or mass transfer efficiency of extractors, especially reciprocating plate extractors.
Solvent extraction processes are well established techniques in the petroleum, pharmaceutical and chemical industries. Indeed, a wide variety of liquid-liquid extraction columns are known in the art. Some of these extractors have fixed internals composed of various types of sieve trays having associated therewith coalescence media, collector-coalescor plates and the like. Some extractors are designed to impart mechanical agitation to the liquids flowing through the extractor in an attempt to improve the mass transfer efficiency of such extractors. For example, pulsating energy is one technique that has been employed for obtaining a high rate of mass transfer in a liquid-liquid extractor. More recently, some extractors have been designed which have reciprocating plates to introduce mechanical agitation since reciprocating plates are more energy efficient than pulsating type extractors columns.
Emulsion formation is a problem associated with all of these types of extractors. For example, the flow limiting phenomena in reciprocating plate extractors results from a build-up or formation of an emulsion of close-packed droplets in certain zones between the plates in the extractor. These emulsion droplets eventually progress through the wrong end of the column and in such instances the extractor is said to be flooded.
In the past, several techniques have been employed to deal with the emulsion phenomena. Thus, for example, to optimize the capacity of reciprocating plate extractors, the technique of increasing the plate spacing in emulsion prone zones of the extractor while providing for smaller spacing between the plates in the balance of the reciprocating plate extractor has been employed.
None of the techniques employed to deal with emulsions has been totally satisfactory, however. Consequently, there remains a need for improved extractors that overcome some of the problems associated with emulsion formation in these extractors. With respect to reciprocating plate extractors, for example, there remains a need for such extractors which have a greater flow capacity than presently achieved with reciprocating plate extractors.